When you plan to build a satellite communication network or use satellites for service transmission, what factors do you choose for satellite transponder resources? In addition to concerns about rental fees, transponder EIRP (effective isotropic radiated power), G/T (system quality factor) and SFD (saturated flux density) main technical indicators, satellite coverage, etc., you will also consider other Factors? What other factors do you need to consider? Which of these factors need to be prioritized? Each satellite has its own characteristics, and each satellite company has its own advantages, and the needs of users are not the same. In order to ensure the stable and normal operation of the satellite network, users should fully understand the relevant information before leasing the transponder resources. This article briefly introduces several factors that need to be taken into account when selecting satellite transponder resources for your reference.
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1 User requirements
1.1 Network Service Scope
Commonly used C-band beams are generally designed to cover a hemispherical beam with a large coverage, while Ku-band beams are generally designed to be small-area coverage area beams or spot beams according to factors such as population density and economic development. The coverage of each satellite is certain, and users need to choose the satellites that can meet the coverage of all stations in the satellite network in accordance with the needs of their own services. Especially for private networks, it is recommended not to pursue excessive satellite coverage. At the same time, in order to save network construction costs, facilitate network management, and reduce satellite link delay, we should first consider and select a satellite to meet the coverage requirements of all stations in the network, and then consider the satellite double-hop approach.
1.2 Working frequency band selection
Synchronous orbit communication satellites typically operate in the C-band (6 GHz/4 GHz) and Ku-band (14 GHz/12 GHz). Compared with the C-band, the Ku-band has the characteristics of small satellite coverage, high satellite EIRP and G/T, smaller antennas under the same conditions, severe rainfall loss, and easy coordination with terrestrial network bands. It cannot be generalized that a certain band is suitable for a certain type of service, and the cost of ground equipment in different bands is also different.
In addition to the standard C and Ku bands, both bands have corresponding extended bands. Relatively speaking, the cost of terrestrial equipment in the extended frequency band is higher, and the cost of the transponder resources may be reduced. In addition, users must also consider the mutual interference effects of the current and future terrestrial wireless networks and extended frequency bands, especially the extended C-band.
2 Business license
The Telecommunications Regulations of the People's Republic of China stipulates that the operation of the satellite transponder for the rental and sale of business must be approved by the Ministry of Industry and Information Technology. In order to protect the rights and interests of users, users must choose a unit or company that has the qualification to operate.
3 satellite orbital
3.1 Ownership of orbital position
The ITU requires the application and registration of orbital positions of synchronous satellites on a national basis. Satellite orbit resources have important strategic significance for a country's political, economic and national defense construction. With the development of satellite communications, the number of satellites in the synchronous orbit has gradually increased, and the orbital resources have become increasingly scarce, and the subsequent competition for orbital resources has become increasingly fierce. Considering the long-term operation of the satellite network, it is recommended to select the satellite resources in the orbital position registered by the Chinese government at the ITU.
Information on the position of the satellite orbit can be found on the official website of the ITU.
3.2 Antenna elevation angle
Selecting the satellites in different orbital positions directly determines the elevation angle of the ground station antenna. The lower the antenna elevation angle, the more susceptible the carrier is to ground signals and the Earth's thermal noise, reducing the G/T value of the ground system. The lower the antenna elevation angle, the higher the transmission distance from the ground station to the satellite, and the free space loss of the carrier increases. The lower the antenna elevation angle, the longer the distance the carrier travels through the rain zone, and the greater the rainfall loss experienced by the Ku-band carrier. Users should try to choose a satellite with a large elevation angle to the antenna in the network.
4 satellite platform
The satellite platform largely determines the performance of the satellite throughout its lifetime. It is true that the purchase of a satellite for any platform is first and foremost a consideration by satellite companies. At present, companies producing commercial communication satellites in the world are mainly concentrated in the United States, Europe and China, and relevant satellite platform information can also be queried on the network. For the user, the main consideration is whether the satellites of the same platform are operating in orbit with the same platform, and whether the satellites of the platform have a well-recognized good on-orbit operation record. If the satellite can't run in the long-term and stable on-orbit, even if there is even better coverage, it is in vain.
5 Repeater Specifications
This indicator may be the most frequently used indicator by users, including EIRP, G/T and SFD parameters of the repeater. Generally speaking, the higher the indicators, the better the performance of the satellite link under certain conditions, the smaller the antenna diameter, or the smaller the power amplifier, the higher the system margin, and the lower the network construction cost. However, when considering these indicators, users must consider other relevant factors at the same time. For example, the increase of indicators may be accompanied by an increase in the cost of transponder rental. For example, satellite companies rely on neighboring satellite coordination requirements or system access requirements, and restrictions on the user's ground station antennas, such as although the indicators have improved, but because of the number of transponders The carrier performance requirements, the link performance of the user service does not necessarily increase accordingly. The high EIRP value does not mean that the user's service carrier is allocated to the satellite radiated power is also high. The size of the SFD is directly related to the setting of each transponder attenuation file, and the SFD corresponding to each transponder is adjustable.
Too much emphasis on the size of the above transponder technical indicators, often end up, and ignore other more important factors affecting network operation. Users should fully understand the meaning of these parameters in order to know their own when choosing a transponder. I hope that users must pay attention to this point.
6 Satellite management and control
For satellite networks or satellite links, to a certain extent, satellite companies are most important for the good management and manipulation of satellites.
6.1 Satellite monitoring and control
The level of the satellite company's measurement and control satellites directly affects the satellite's coverage performance, satellite life, attitude control, orbital accuracy, and satellite failure rate. Every user wants their network to run on a long-term stable, well-covered, orbit-accurate satellite and use it to conduct their own business. Before selecting satellite transponders, users are strongly advised to have an understanding of the on-orbit operation of the relevant satellites, and to select satellites from satellite companies with high levels of satellite measurement and control capabilities and good satellite orbital records.
Users can visit the satellite company's measurement and control center and communicate with existing users on the star to conduct targeted understanding.
6.2 Satellite orbital accuracy
Satellites in geosynchronous orbits are subject to drift by the influence of the sun, the gravitation of the moon, the elliptical shape of the Earth, and many other natural factors. The satellite company's monitoring and control center will periodically control the satellites in the north-south direction and the east-west direction in order to keep the orbital drift of the satellite within a certain range. Most satellite companies can maintain satellite orbital accuracy to better than ±0.05 degrees.
When the satellite drifts away from the beam center of the terrestrial antenna, the satellite transponder coverage parameters will not be fully utilized because of the reduced gain of the terrestrial antenna. It is estimated that the ground antenna gain decreases by a factor of several times when the satellite drifts by 0.1 degrees. Moreover, high-band and large-caliber antennas are much more affected than low-band and small-caliber antennas.
Satellite orbital accuracy can be consulted with satellite companies.
6.3 Neighbor coordination
The shortage of orbital resources has caused the orbital spacing between adjacent satellites to become smaller and smaller, which in turn has increased the possibility of adjacent star interference and also increased the constraints of satellite links.
In order to reduce the possibility of neighboring satellite interference, satellite companies will make commitments and requirements in the neighboring star coordination document to limit the upstream and downstream antenna aperture and carrier power spectral density on adjacent satellites, so that the transponder cannot be fully used in actual use. Take advantage of its design performance. If the uplink and downlink interference estimates from neighboring stars are insufficient, the carrier-to-interference ratio of the satellite link will be reduced, resulting in a system margin in the actual link being lower than the link budget.
In accordance with ITU's principle of coordination, the priority of coordination depends on the date of publication of the satellite coordination information, not the date of satellite launch. For reasons of competition, the party with the coordination priority usually imposes more stringent restrictions on the neighboring star business. Therefore, when selecting a satellite transponder, the user should try to understand the coordination result of the neighboring satellite of the relevant satellite, and should select the satellite that has completed the on-orbit coordination and has the priority in the orbit. On the official website of the ITU, the coordination status of the relevant satellites can be queried.
6.4 Satellite life
If the user plans to build a satellite network that requires long-term operation, it is recommended to select a satellite with a remaining life of not less than 5 years, otherwise the user will soon face the problem of business turnaround or network adjustment. There is basically no need to consider this factor for temporary use of the business.
7 backup capabilities
For satellite networks that are scheduled to run for a long time, users need to consider the emergency backup capabilities of the network. For space segment resources, choose satellites with repeater resource backup capabilities and satellite companies with alien emergency backup capabilities. Moreover, the orbital position of the backup star should not be too large, which facilitates the rapid adjustment of the antenna pointing.
For temporary use of services, it is recommended that users choose satellites with repeater backup capabilities.
8 Summary
In general, a satellite operator may not be able to provide all of the above information to the user, and the user may not be able to select satellite transponder resources that meet all of the above requirements. This paper wants to emphasize that, considering the development of satellite communication industry and satellite manufacturing industry, the difference in coverage performance between satellites is often not too big. The determinants that affect the normal operation of users' satellite networks are also focused on satellite control and neighbors. Star coordination, repeater management, interference processing and other aspects. It is recommended that users select the satellite transponder resources in addition to comparing the coverage performance of the satellites, but also pay full attention to the above aspects.
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